Reversible pump-turbine system

ABSTRACT

A reversible pump-turbine system having a discharge adjustment device such as guide vanes, which make it possible to safely stop a pump turbine at the time of emergency shutdown in a generating mode by performing a close operation using an inlet valve even if abnormality has occurred with the guide vanes, without causing abnormal water hammer. Also, at the time of pump mode emergency shutdown, reverse rotation can be prevented even if abnormality occurs in the guide vanes, and it is possible to achieve a safe stop while reducing the loads/stresses to the reversible pump-turbine.

TECHNICAL FIELD

This invention relates to a reversible pump-turbine system provided witha water amount adjustment device, such as guide vanes, and particularlyto a reversible pump-turbine provided with an inlet valve.

BACKGROUND ART

In a conventional reversible pump-turbine, guide vanes are caused toclose down with a pattern as shown by the dotted lines in FIGS. 11 (a)and (b) the time of generation mode emergency shutdown and pump modeemergency shutdown. Description will first be given for generation modeemergency shutdown. In this situation, the guide vanes are suddenlyclosed at the same time as a circuit breaker of an electrical generatoris opened. When the initial open amount is Yt0, the guide vanes areclosed to open amount Yt1 at a first restricted rate (rapid closurerate) previously set for use in the generation mode that has been, asshown by the dotted lines in FIG. 11(a) and from that point it isautomatically switched to a second previously set restricted rate(closure rate after change) for use in the generation mode, and afterthat the guide vanes are closed at that rate. These first and secondrestricted rates are rendered by restricting an amount of passing oil ina control valve for a guide vane servo motor driving the guide vanes. Ifthe opening amount becomes less than Yt2, a fully closed end cushion ofthe guide vane servo motor is actuated, which causes the closure rate tobe lowered even further, as shown by the dotted lines in FIG. 11(a). Thereason for automatically switching from the first restricted rate (rapidclosure rate) to the second restricted rate (closure rate after change)in this way with the opening amount at Yt1 is described in detail inJapanese Patent Laid-open Publication No. Sho. 61-47981, etc., by theinventor of this invention. That is, as a result of raising and loweringthe unit speed Ni after the circuit breaker is opened, the operatingpoint trajectory of the pump turbine breaks into S0 to S1 and S1 to S3,the latter moving in a S0-called S shaped characteristic(s) of the pumpturbine, as shown by the dotted line in FIG. 7, and because tracing ofthe S-shaped characteristics in a direction of reduced discharge iscommenced there is a need to switch the guide vanes to a slow closurerate before the commencement. What is meant by the S-shapedcharacteristic here is the portion of dQ1/dN1>0 as shown in FIG. 5.

Next, emergency shutdown in a pumping mode will be described. The guidevanes are also closed rapidly at the same time as the circuitbreaker isopened. One criteria for determining the guide vane closure pattern inthis case will be described using FIG. 3. In the case where the guidevanes are closed rapidly, as shown by the solid lines in FIG. 3(b) therotation speed is Na when the guide vanes become fully closed, while therotation speed falls to Na′ at the time of fully closed when the guidevanes is closed slowly, as shown by dotted lines in FIG. 3(b). FIG. 4shows the relationship between time required for guide vanes to be fullyclosed and the rotation speed when the guide vanes are fully closed. Aswill be understood better from FIG. 4, if the time required to fullyclose the guide vanes becomes a long time, that is if the closure rateof the guide vanes is slow, Na′ no longer has a positive value but has aminus value. What this actually means is that reverse rotation may arisein the pump mode. This reverse rotation is extremely damaging due towear on a thrust bearing.

Another criterion determining a guide vane closure pattern at the timeof emergency shutdown in the pump mode will be described using FIGS.8(a) and 8(b).

This description will be given with X0 and Xa as guide vane openingamounts, X0>Xa. A trajectory of the operating point when the guide vanesare closed rapidly is shown by the dotted line in FIG. 8(a). By way ofcomparison, the case when the guide vanes are closed slowly is shown bythe dotted line in FIG. 8(b). Reverse discharge, that is, reverse flow,arises when rotation speed is positive, namely during pump rotation.Even though a reversible pump-turbine has pump rotation, the operatingcondition becomes to allow turbine flow as accompanied with oscillationsand noises. The problem is here that if the guide vane opening amount istoo large when reverse flow appears, the operating conditions becomebad. Depending on the situation, the reversible pump-turbine can alsobecome damaged. Even further a worse condition than in FIG. 8(b) ispossible. If the guide vanes are closed more slowly reverse rotationalso will occur even in the pump mode. The guide vanes will be fullyclosed before long no matter how slowly the guide vanes are closed, andso the operating points finally converge at (0, 0).

The guide vane closure pattern for pumping mode emergency shutdown asdescribed above is determined not to allow reverse rotation, and sodetermined that reverse flow is suppressed to the minimum.

The above describes conventional technology relating to guide vaneclosure patterns, and on the other hand conventional technology relatingto inlet valve closure patterns is shown in FIGS. 9(a) and 9(b). Thatis, with respect to an inlet valve, the maximum closure rate isdetermined as a rate close to the second control rate and lower than thefirst control rate for the guide vanes at the time of emergency shutdownin the generating mode, and this rate is used for both the generatingmode and the pumping mode. That is, the rate at the time of generatingmode emergency shutdown and the rate at the time of pumping modeemergency shutdown are made the same. Strictly speaking, the load torqueacting on the inlet valve is different in the generating mode emergencyshutdown and the pumping mode emergency shutdown, which means that, evenif the inlet valve closing rate is set to the same rate at the time of adry test, there are slight differences when the inlet valve is operatedin water, but these can be ignored. A reversible pump-turbine that isthe subject of the present invention generally carries out flow amountadjustment using the guide vanes, and so does not cover the case whereusual discharge adjustment at the time of start-up etc. is carried outusing an inlet valve. An inlet valve is considered which is to be openedprior to opening the guide vanes and to be closed after closing theguide vanes, and used in maintenance and inspection operations of thereversible pump-turbine.

However, in adopting the closure patterns of the above describedconventional technology as closely as possible, it will be understoodthat the inlet valve can not achieve the desired back-up function at thetime of pumping mode emergency shutdown. That is, consider the case ofFIGS. 2(a) and 2(b) where the guide vanes have failed and can not beclosed at all.

This can be understood on the basis of an extent to which the inletvalve, can carry out the water flow reducing function in place of theguide vanes. The inlet valve is closed in the pump mode at the same slowclosure rate as in the generating mode,and naturally reverse rotationcan not be avoided more or less. A typical example of the relationshipbetween the time required to fully close the inlet valve and therotation speed at the time when the inlet valve is fully closed will bedescribed using FIG. 4. It is assumed that the guide vane closurepattern is as shown by the solid line in FIG. 3(b) and the inlet valveclosure pattern is as shown by the dotted line in FIG. 3(b). In such acase, if it is assumed that the guide vanes have failed, the rotationspeed at the time the inlet valve is fully closed is lowered to Na′ anddoes not lead to reverse rotation. However, As shown in FIG. 4, if thetime required to fully close the inlet valve is further prolonged therotation speed at the time the inlet valve is fully closed is loweredrapidly, and if the time required to fully close the inlet valve becomeslonger than Tax, reverse rotation becomes a possibility. In the abovedescribed conventional art, for example, even if reverse rotation hasbeen avoided, a large amount of reverse flow is possible transientlyduring positive rotation, as shown in FIG. 8(b), and clearly thereversible pump-turbine is exposed to a dangerous condition. On theother hand, If the closure rate of the inlet valve is increased, theinlet valve is allowed to play a part in substantially throttlingdischarge at the time of generating mode emergency shutdown, anddepending on the situation when the operation point of the pump turbineenters the S-shaped characteristics there is a possibility of abnormalwater hammer.

The object of the present invention is to provide a safe system thateliminates the drawbacks of the above described related art, and enablesthe back-up function of discharge adjustment by the inlet valve at thetime of emergency shutdown in the pump mode, but on the other hand doesnot have any harmful effect in the generating mode.

DISCLOSURE OF THE INVENTION

The present invention provides a reversible pump-turbine system providedwith an inlet valve and a discharge adjustment device for controllingadjustment of the discharge of the reversible pump-turbine which isconnected to a generator-motor, and further comprises inlet valveclosure means for closing the inlet valve at a rate slower than a normalclosure rate of the discharge adjustment device at the time of pumpingemergency shutdown, and the closure rate of the inlet valve is switchedaccording to the operation mode of the reversible pump-turbine.

The present invention further provides automatic closure means forclosing the inlet valve at a higher rate than the generating modeemergency shutdown, when a power supply to the generator-motor isdisconnected or at the time of pumping mode emergency shutdown forcarrying out a stop operation in a condition where the generator-motorpower supply is lost.

Still further, in the present invention, at the time of pumpingemergency shutdown for executing a stop operation accompanyingdisconnection of a drive power supply or in a power failure situation,the inlet valve is closed in a period of time longer than the timenormally needed for the discharge adjustment device to substantiallycomplete closure, and even when closure of the discharge adjustmentdevice is impossible, inlet valve closure is carried out in asufficiently short time period so that the rotation speed of thereversible pump-turbine at the time of closure of the inlet valve doesnot lead to reverse rotation.

The present invention further provides means for, at the time of pumpingemergency shutdown, for executing a stop operation accompanyingdisconnection of a power supply of a drive electric motor or in a powerfailure situation, substantially completing inlet valve closure in aperiod of time longer than the time normal needed for the dischargeadjustment device to substantially complete closure, and, when closureof the discharge adjustment device is impossible, even if reverserotation of the reversible pump-turbine becomes temporarily allowed,closing the inlet valve at a speed sufficient to lower the opening areaof the inlet valve at the instant of reverse rotation to an openingequivalent to or less than the opening of the discharge adjustmentdevice required to start the pump turbine from standstill in thegeneration mode.

The present invention further completes inlet valve closure in a timeperiod longer than a time period required for the discharge adjustmentdevice to substantially complete closure in normal operation, at thetime of generating mode emergency shutdown.

Still further, at the time of pumping emergency shutdown the presentinvention carries out inlet valve closure so as to constantly keepopening area of the inlet valve larger than the opening area of thedischarge adjustment device all the way in normal operation, andbesides, even if closure of the discharge adjustment device isimpossible, inlet valve closure is carried out to an extent that doesnot lead to reverse rotation at the instant of completion of inlet valveclosure.

Also, in the present invention, at the time of generating mode emergencyshutdown accompanying disconnection of the output of the generator,inlet valve closure is executed so as to constantly keep the openingarea of the inlet valve larger than the opening amount of the dischargeadjustment device all the way in normal operation.

The present invention is further provided with a low speed detector fordetecting that the rotation speed during pumping operation has fallenbelow a rated value (in the case of the adjustable speed machine, belowan appropriate value according to the operating conditions at thattime), and means for automatically switching so as to close the inletvalve at a high rate faster than that at the time of generating modeemergency shutdown, on condition that the low speed detector hasoperated.

The present invention is still further provided with a low speeddetector for detecting that the rotation speed during pumping operationhas fallen below a rated value (in the case of the adjustable speedmachine, below an appropriate value according to the operatingconditions at that time), and a failure detector for detecting thatclosing operation of the flow rate adjustment device such as the guidevanes have not been carried out at a specified rate, and has means forautomatically switching so that the inlet valve is closed at a fast ratefaster than the rate at the time of generating mode emergency shutdownon condition that the speed low detector and the failure detector haveoperated.

According to the present invention, by switching the closure rate of aninlet valve according to the operating mode, even if an abnormalityarises in a discharge adjustment device, it is possible to achievefailsafe operation on the inlet valve side according to the operatingmode at the time of the abnormality.

Further, according to the present invention, by slowing the inlet valveclosure rate to less than that of a guide vane second restricted rate inthe generating mode, abnormal water hammer is prevented even when theoperation point of the pump turbine is tracing down the S-shapedcharacteristic, while a very fast closure rate enabling avoidance orreduction of reverse rotation and large reverse flow with positiverotation can be selected in the pumping mode.

Also, if the inlet valve is closed at the time of pumping emergencyshutdown in a time period that is longer than the time the guide vanestake to close under normal closure, or if the inlet valve is closed sothat inlet valve opening area is kept larger than the guide vane openingarea all the way during normal closure, it becomes possible for theinlet valve to play a part in the failsafe operation while reducing orpreventing the possibility of the inlet valve being used in substantialadjustment of discharge during normal operation of the guide vanes.

According to the present invention, even in the case of pumpingemergency shutdown, if the inlet valve is closed at a sufficiently fastrate so that reverse rotation does not occur when the inlet valve isfully closed, it is possible to prevent reverse rotation after that.

Further, according to the present invention, at the time of pumpingemergency shutdown, it is possible to limit actual damage to the machineby limiting the opening of the inlet valve at the instant of rotationreversal smaller than the opening of the guide vanes required forstarting in the generating mode, even if reverse operation isunavoidable due to a failure of the discharge adjustment device.

For reduction of the discharge at the time of pumping mode emergencyshutdown, there are three governing factors, that is, closing of thedischarge adjustment device, closing of the inlet valve, and lowering ofthe rotation speed of the reversible pump-turbine itself, but of thesefactors, lowering of the rotation speed of the reversible pump-turbineitself is extremely significant. That is, even if the inlet valve isclosed at a rapid closure rate, the extent to which it participates inthrottling of discharge is not significant. Specifically, in this case,the object of the present invention can be achieved without exerting alarge differential pressure on the inlet valve, i.e. without difficulty.

In other words it would be reasonable to carry out switching of theinlet valve for rapid closure only in the case where lowering of therotation speed of the reversible pump-turbine itself predominantlyaffects throttling of discharge.

Also, a low speed detector can be used in place of direct detection ofpower failure conditions, where the motor input power is lost ordisconnected during the pumping operation, since the speed immediatelydrops. Further, if a failure detector is provided to detect a closingfailure of the discharge adjustment device not in accordance with thedesired rate, it is possible to carry out inlet valve rapid closure onlyin the case where an AND condition is satisfied with respect tooperation of the low speed detector and operation of the failuredetector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) are drawings showing an inlet valve closure methodof the present invention.

FIGS. 2(a) and 2(b) are drawings showing an inlet valve closure methodof the present invention in the case where guide vane closure becomesimpossible.

FIGS. 3(a) and 3(b) are drawings showing the relationship between guidevane/inlet valve closure rate and rotation speed lowering amount in thecase of pumping mode emergency shutdown.

FIG. 4 is a drawing showing the relationship between time required forguide vane/inlet valve closure and rotation speed lowering amount in thecase of pumping mode emergency shutdown.

FIG. 5 is a drawing showing a four quadrant N1−Q1 characteristic of areversible pump-turbine.

FIGS. 6(a) and 6(b) are drawings showing the relationship between inletvalve closure rate and rotation speed lowering amount in the case whereguide vane closure has become impossible at the time of pumping modeemergency shutdown in the related art.

FIG. 7 is a drawing showing a trajectory of operation point of a pumpturbine at the time of generating mode emergency shutdown.

FIGS. 8(a) and 8(b) are drawings showing a trajectory of operation pointat the time of pumping mode emergency shutdown.

FIGS. 9(a) and 9(b) are drawings showing an inlet valve closure methodof the related art.

FIG. 10 shows an example of the specific circuit structure for carryingout the inlet valve closure method of the present invention.

FIGS. 11(a) and (b) are drawings showing a pattern of guide vanes causedto close down.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in more detail with reference tothe attached drawings.

FIGS. 1(a) and (b) show an embodiment of the present invention. Thesedrawings show the emergency shutdown conditions for a generating modeand a pumping mode, and in the drawings a dotted line represents guidevane opening amount while a solid line represents inlet valve openingamount. At the time of generating mode emergency shutdown, the inletvalve is closed at a rate that is slightly lower than a secondrestricted rate for the guide vanes. If the inlet valve is closed inthis manner, it will be safe even if, guide vane closure becomesimpossible. This is because it is possible to avoid abnormal waterhammer even if the operating point of the reversible pump-turbine istracing down the S-shaped characteristic. Since closure of the inletvalve is slow compared to the desired guide vane closure, the timeperiod for which the rotation speed is high inevitably becomes longer,but it does not lead to damage of the reversible pump-turbine. Since, inthe case of a reversible pump-turbine, raising of rotational speed issubstantially limited by the existence of the S-shaped characteristic,it does not lead to an abnormal speed increase. Therefore, in agenerating mode the back-up function of the inlet valve takes effect torealize failsafe operation. In the example of FIG. 1(a), a cushioning isprovided to reduce closing speed of the inlet valve at the closed endbelow Xt1 but it is not necessary for the purpose of the presentinvention.

On the other hand, according to the reversible pump-turbine system ofthe present invention, at the time of pumping mode emergency shutdown,the inlet valve is closed at a faster rate than a second limit rate forthe guide vanes in the above described generating mode up to the pointwhere the opening amount is Xp1, as shown in FIG. 1(b). From openingamount Xp1, closure is automatically switched to a lower rate. Thischange in the closure rate is to prevent water hammer caused by suddenthrottling of water already flowing through the pump turbine in theturbine direction as a result of flow reversal. With the slower closurerate of the related art, this change is not necessary. In the presentinvention, by carrying out control in this way, it becomes possible tomaintain the rotation speed at the time of the inlet valve fully closedat a positive value including a desired margin, as shown by Na′ in FIG.4, or to prevent at least reverse rotation.

As another embodiment of the present invention, for example, when anabnormality arises in pumping operation mode, it is possible to preventan undesirable condition that the pump turbine comes in a reverse flowoperation before the inlet valve has been closed to a safe opening muchsmaller than Yb in FIG. 5. It is also possible to have completed closureof the inlet valve down to an opening amount equivalent to a guide vaneopening setting for generating mode starting, before the rotationreversal.

If reverse rotation occurs with an opening amount larger than the above,operating conditions of the pump turbine become rough with largevibrations and noises. As a result, in the present invention, mechanicalsafety is ensured even when undesirable transfer to a substantialgenerating mode can not be avoided, as described above.

FIG. 10 shows a hardware example for realizing the inlet valve closuremethod of the present invention. In this drawing, reference numeral 1 isan open or close signal to be supplied to a distributing valve for usewith an inlet valve drive servo motor, and is +β(p.u.) for an openoperation and −β(p.u.) for a close operation. Reference numeral 3 is anelement for judging whether it is a close operation or an openoperation, i.e. if a plunger of the distributing valve is moved up thenan open side port is connected, while if the plunger is moved down aclose side port is connected. Reference numeral 9 is an inlet valveopening speed setting element. Wa<β. Specifically, when an openoperation command is inputted, the speed of movement of the inlet valveservo motor is limited to Wa.K(pu/sec). In other words, upward movementof the plunger of the distributing valve is mechanically limited, and/oran amount of oils passing through the open side port of the distributingvalve is throttled.

Reference numeral 6 is a judging element for carrying out inlet valverapid closure of the present invention limited to the case when inputpower during pumping operation is lost or disconnected. Normally, it isconnected to the upper side and the closure rate is limited toWb.K(p.u./sec) through a first closure rate limiting element 10. In theevent that input power during pumping operation is lost or disconnectedthe judging element 6 is connected to the lower side and the closurerate is limited to Wc.K(p.u./sec) through the second closure ratelimiting element 11.

What the above actually means is that downward movement of thedistributing valve plunger is mechanically restricted, and/or an amountof oil passing through the close side port of the distributing valve isthrottled in response to the previously described operating mode. Here,|Wb|<|β|, |Wc|<|β|.

Reference numeral 18 is the sum of outputs from three control elements12, 13 and 14, but a selected control element is normally one from thesethree, and output from an element that is OFF is zero so no interferenceoccurs among the three.

According to the present invention, an inlet valve performs a backupfunction for the guide vanes at the time of emergency shutdown, in bothoperating modes, namely in of generating and in pumping. At the time ofgenerating mode emergency shutdown, abnormal water hammer arising due toa S-Shaped characteristic does not occur, even if closure of the guidevanes is not possible. Also, at the time of pumping mode emergencyshutdown, even if closure of the guide vanes is not possible reverserotation is not permitted or at least a large reverse discharge withpositive rotation or reverse rotation under an excessively large openingis prevented, damage to the reversible pump-turbine and related devicesis prevented and it is possible to maintain safety with minimumrestriction.

What is claimed is:
 1. A reversible pump-turbine system provided with aninlet valve and a discharge adjustment device for controlling adjustmentof a discharge of a reversible pump-turbine connected to agenerator-motor, comprising: inlet valve closure means for closing theinlet valve at a rate slower than a normal closure rate of the dischargeadjustment device at the time of emergency shutdown, wherein the closurerate of the inlet valve is switched according to an operating mode ofthe reversible pump-turbine.
 2. The reversible pump-turbine system asdisclosed in claim 1, further comprising: automatic closure means forclosing the inlet valve at a higher rate than generating mode emergencyshutdown when a power supply to the generator-motor is disconnected orat the time of pumping mode emergency shutdown for carrying out a stopoperation in a condition where the generator-motor power supply is lost.3. The reversible pump-turbine system as disclosed in claim 2, whereinat the time of pumping emergency shutdown, means are provided forexecuting a stop operation accompanying disconnection of a power supplyof a drive power supply or in a power failure situation, for carryingout inlet valve closure in a period of time longer than the timenormally needed for the discharge adjustment device to substantiallycomplete closure, and when closure of the discharge adjustment device isimpossible, for carrying out inlet valve closure in a time period inwhich rotation speed of the reversible pump-turbine at the time ofclosure of the inlet valve has not be reversed.
 4. The reversiblepump-turbine system as disclosed in claim 2, wherein, at the time ofpumping emergency shutdown, means are provided for executing a stopoperation accompanying disconnection of a power supply ofgenerator-motor or in a generator-motor power supply failure situation,for substantially completing inlet valve closure in a period of timelonger than a time needed for the discharge adjustment device in normalcondition to substantially complete closure, and when closure of thedischarge adjustment device is impossible, for closing the inlet valveat a speed sufficient to lower the opening area of the inlet valve atthe time when reverse rotation occurs to a set opening amount, or less,of the discharge adjustment device at the time of generation modestarting.
 5. The reversible pump-turbine system as disclosed in claim 3,wherein at the time of generating mode emergency shutdown, means areprovided for carrying out inlet valve closure in a time period longerthan a time period required for the discharge adjustment device innormal condition to substantially complete closure.
 6. The reversiblepump-turbine system as disclosed in claim 2, wherein, at the time ofpumping emergency shutdown, means are provided for carrying out inletvalve closure so as to keep the opening area of the inlet valve largerthan the opening area of the discharge adjustment device closing innormal condition, and if closure of the discharge adjustment devicebecomes impossible, inlet valve closure is carried out at such a ratethat does not lead to reverse rotation of the reversible pump turbinebefore completion of closure.
 7. The reversible pump-turbine system asdisclosed in claim 3, wherein, at the time of generating mode emergencyshutdown accompanying disconnection of output of the generator-motor,means are provided for execution of inlet valve closure so as to keep anopening area of the inlet valve larger than an opening area of thedischarge adjustment device closing in normal condition.
 8. A reversiblepump-turbine system provided with an inlet valve and a dischargeadjustment device for controlling adjustment of a discharge of areversible pump-turbine connected to a generator-motor, comprising:inlet valve closure means for closing the inlet valve at a rate slowerthan a normal closure rate of the discharge adjustment device at thetime of emergency shutdown, wherein the closure rate of the inlet valveis switched according to an operating mode of the reversiblepump-turbine; and further comprising: a low speed detector for detectingthat rotation speed during pumping operation has fallen below a ratedvalue; and closure means for closing the inlet valve at a high ratefaster than the closure rate at the time of generating mode emergencyshutdown, in response to a signal from the low speed detector.
 9. Areversible pump-turbine system provided with an inlet valve and adischarge adjustment device for controlling adjustment of a discharge ofa reversible pump-turbine connected to a generator-motor, comprising:inlet valve closure means for closing the inlet valve at a rate slowerthan a normal closure rate of the discharge adjustment device at thetime of emergency shutdown, wherein the closure rate of the inlet valveis switched according to an operating mode of the reversiblepump-turbine; and further comprising: a low speed detector for detectingthat the rotation speed during pumping operation has fallen below arated value, a failure detector for detecting that a closing operationof the discharge adjustment device has not been carried out at aspecified rate; and closure means for closing the inlet valve at a fastrate faster than the rate at the time of generating mode emergencyshutdown in response to operation of the low speed detector and thefailure detector.
 10. A reversible pump-turbine system provided with aninlet valve and a discharge adjustment device for controlling adjustmentof a discharge of a reversible pump-turbine connected to agenerator-motor, comprising: a controller for closing the inlet valve ata rate slower than a normal closure rate of the discharge adjustmentdevice at the time of emergency shutdown, wherein the closure rate ofthe inlet valve is switched according to an operating mode of thereversible pump-turbine.
 11. The reversible pump-turbine system asdisclosed in claim 10, further comprising: a controller for closing theinlet valve at a higher rate than generating mode emergency shutdownwhen a power supply to the generator-motor is disconnected or at thetime of pumping mode emergency shutdown for carrying out a stopoperation in a condition where the generator-motor power supply is lost.12. In a reversible pump-turbine system provided with an inlet valve anda discharge adjustment device, a method of controlling adjustment of adischarge of a reversible pump-turbine connected to a generator-motor,comprising the steps of: closing the inlet valve at a rate slower than anormal closure rate of the discharge adjustment device at the time ofemergency shutdown, wherein the closure rate of the inlet valve isswitched according to an operating mode of the reversible pump-turbine.13. The method of claim 12, further comprising the steps of: closing theinlet valve at a higher rate than generating mode emergency shutdownwhen a power supply to the generator-motor is disconnected or at thetime of pumping mode emergency shutdown for carrying out a stopoperation in a condition where the generator-motor power supply is lost.14. The method of claim 13 further comprising the steps of, at the timeof pumping emergency shutdown, executing a stop operation accompanyingdisconnection of a power supply of a drive power supply or in a powerfailure situation, carrying out inlet valve closure in a period of timelonger than the time normally needed for the discharge adjustment deviceto substantially complete closure, and when closure of the dischargeadjustment device is impossible, carrying out inlet valve closure in atime period in which rotation speed of the reversible pump-turbine atthe time of closure of the inlet valve has not be reversed.
 15. Themethod of claim 13 further comprising the steps of, at the time ofpumping emergency shutdown, executing a stop operation accompanyingdisconnection of a power supply of generator-motor or in agenerator-motor power supply failure situation, substantially completinginlet valve closure in a period of time longer than a time needed forthe discharge adjustment device in normal condition to substantiallycomplete closure, and when closure of the discharge adjustment device isimpossible, closing the inlet valve at a speed sufficient to lower theopening area of the inlet valve at the time when reverse rotation occursto a set opening amount, or less, of the discharge adjustment device atthe time of generation mode starting.
 16. The method of claim 14 furthercomprising the step of, at the time of generating mode emergencyshutdown, carrying out inlet valve closure in a time period longer thana time period required for the discharge adjustment device in normalcondition to substantially complete closure.
 17. The method of claim 13further comprising the step of, at the time of pumping emergencyshutdown, carrying out inlet valve closure so as to keep the openingarea of the inlet valve larger than the opening area of the dischargeadjustment device closing in normal condition, and if closure of thedischarge adjustment device becomes impossible, carrying out inlet valveclosure at such a rate that does not lead to reverse rotation of thereversible pump turbine before completion of closure.
 18. The method ofclaim 14 further comprising the step of, at the time of generating modeemergency shutdown accompanying disconnection of output of thegenerator-motor, executing inlet valve closure so as to keep an openingarea of the inlet valve larger than an opening area of the dischargeadjustment device closing in normal condition.